Aldehyde synthesis

Abstract

Aldehydes are produced by cleaving 2,2-dialkyltetrahydropyrans bearing two hydrogen atoms in the sixth position with a strong acid. The 2,2-dialkyltetrahydropyran can be formed in situ by contacting the strong acid with a primary 6-alken-1-ol having at least one methyl group in the fifth position so that cyclization occurs.

I claim: 
     
       1. A process of producing an alkyl-substituted alkanal which comprises contacting a 2,2-di-lower-alkyl tetrahydropyran bearing two hydrogen atoms in the sixth position with a strong acid selected from the group consisting of phosphoric acid, polyphosphoric acid, benzene sulfonic acid, toluene sulfonic acid, hydrochloric acid, and sulphuric acid at a temperature within the range of about 50° C. to about 200° C. at which said 2,2-di-lower-alkyl tetrahydropyran is cleaved and a 1,5-hydride shift occurs so that an alkyl-substituted alkanal is produced. 
     
     
       2. A process according to claim 1 wherein said strong acid is phosphoric acid. 
     
     
       3. A process according to claim 1 wherein said 2,2-di-lower-alkyl tetrahydropyran is formed in situ by contacting said strong acid with a primary 6-alken-1-ol having one methyl group and one hydrogen atom in the fifth position so that a 2,2-di-lower-alkyl tetrahydropyran is formed via (i) protonation in the seventh position, (ii) formation of a tertiary carbonium ion in the fifth position via a 1,2-hydride shift and (iii) intramolecular ring closure and proton elimination involving the oxygen atom and the tertiary carbonium ion. 
     
     
       4. A process according to claim 1 wherein said 2,2-di-lower-alkyl tetrahydropyran is formed in situ by contacting said strong acid with a primary 6-alken-1-ol having two methyl groups in the fifth position so that a 2,2-di-lower-alkyl tetrahydropyran is formed via (i) protonation in the seventh position, (ii) formation of a tertiary carbonium ion in the fifth position via a 1,2-methyl shift and (iii) intramolecular ring closure and proton elimination involving the oxygen atom and the tertiary carbonium ion. 
     
     
       5. A process according to claim 3 wherein said acid is phosphoric acid. 
     
     
       6. A process according to claim 4 wherein said acid is phosphoric acid. 
     
     
       7. A process according to claim 2 performed at a temperature of about 90° to about 100° C. 
     
     
       8. A process according to claim 2 performed at a temperature of at least about 90° C. 
     
     
       9. A process according to claim 3 wherein said 6-alken-1-ol is 5-methyl-6-hepten-1-ol so that said 2,2-dialkyltetrahydropyran is 2-ethyl-2-methyltetrahydropyran and said alkanal is 5-methylheptanal. 
     
     
       10. A process according to claim 4 wherein said 6-alken-1-ol is 5,5,6-trimethyl-6-hepten-1-ol so that said 2,2-dialkyltetrahydropyran is 2-methyl-2-tert-butyl-tetrahydropyran and said alkanal is 5,6,6-trimethylheptanal.